Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, a multifunction peripheral having a copy function and a print function, and a facsimile. In particular, the present invention relates to an image forming apparatus having a function of reversely conveying a sheet to form images on both sides of the sheet while the sheet is conveyed.
Description of the Related Art
A conventional image forming apparatus such as a copying machine, a printer, a multifunction peripheral having a copy function and a print function, and a facsimile is provided with a function of printing on both sides of a sheet. Two-sided printing is generally performed by a two-sided discharge mechanism near a discharge tray.
In the case of one-sided printing, a sheet on which printing has been completed is discharged onto a discharge tray by a discharge roller pair and is stacked thereon. In the case of two-sided printing, a sheet on which printing has been completed on a first side is switched back by a reverse roller pair, fed again to a two-sided printing conveyance path, and then conveyed to a printing process for a second side thereof.
The above operations are performed by a drive mechanism which causes each of the conveyance roller pairs to rotate normally (forward) or reversely, and a switching mechanism which switches a conveyance path by using a flipper. To simplify the apparatus, which has been required in recent years, it is important to cause the mechanisms to operate in conjunction with each other and to achieve a reduction in the number of components of the entire apparatus.
Japanese Patent Application Laid-Open No. 2000-26002 discusses a configuration for performing a sheet discharge operation and a sheet reversal operation by one driving roller and two driven rollers (hereinafter referred to as triple rollers as appropriate). Japanese Patent Application Laid-Open No. 2012-140200 discusses a configuration for performing a sheet discharge operation and a sheet reversal operation by one conveyance roller pair.
However, in the configuration discussed in Japanese Patent Application Laid-Open No. 2000-26002, when the reversal operation is performed by the conveyance roller pair, a sheet on a discharge tray provided near the conveyance roller pair may be entangled therein, causing the sheet to move backward, resulting in conveyance failure.
FIG. 1 is a schematic sectional view of a configuration of a conventional two-sided discharge mechanism 10 based on Japanese Patent Application Laid-Open No. 2000-26002. As illustrated in FIG. 1, the conventional two-sided discharge mechanism 10 includes triple rollers 11 for performing a discharge operation and a reversal operation, and a conveyance guide 12 inside the apparatus. In FIG. 1, a sheet 13 discharged by the two-sided discharge mechanism 10 cannot be completely stacked on a discharge tray 14 and remains near the conveyance roller pair.
When the reversal operation is performed in this state, the conveyance roller pair rotates in a direction indicated by solid line arrows illustrated in FIG. 1, which is opposite to a direction of when the discharge operation is performed. At this time, the sheet 13 receives a conveyance force from the conveyance roller pair, and is conveyed in a direction indicated by a dash-dot line illustrated in FIG. 1. As a result, the sheet 13 moves backward to the conveyance path inside the image forming apparatus. Occurrence of such a backward movement may cause a phenomenon in which the sheet 13 gets caught by a step portion 15 of the conveyance guide 12 through a path indicated by a dotted line arrow illustrated in the conveyance path, or may cause a sheet-passing failure due to interference with a subsequent sheet (not illustrated) in the conveyance path during continuous printing.
In the configuration discussed in Japanese Patent Application Laid-Open No. 2000-26002, there is no member having a function of preventing the sheet 13 from moving backward, near the triple rollers 11. Therefore, part of stacked sheets may come into contact with the conveyance roller pair, causing the above phenomenon to occur.
According to Japanese Patent Application Laid-Open No. 2012-140200, there is provided a regulation member protruding into the discharge tray area, thereby preventing a stacked sheet from moving backward. However, Japanese Patent Application Laid-Open No. 2012-140200 does not discuss the prevention of a stacked sheet from moving backward when triple rollers are used. Further, in the configuration discussed in Japanese Patent Application Laid-Open No. 2012-140200, the regulation member is located much below the nip portion between the discharge roller pair. Thus, in a case where a sheet cannot be completely discharged and is in contact with the discharge roller pair as illustrated in FIG. 1, the effect of the regulation member cannot be attained, and there exists an area where the backward movement cannot be prevented.